It is generally accepted that there has been an increase in the prevalence of dental fluorosis in both negligibly- and optimally-fluoridated communities in the United States. Data are available concerning the contribution various fluoride sources have made to this increase in prevalence. In contrast, little data are available concerning the possible time periods of susceptibility. Identification of the time periods of susceptibility, as well as the sources of fluoride, will make it possible to achieve the maximum level of caries prevention while minimizing the risk of dental fluorosis. The goal of this study is to expand upon the data collected by earlier investigators utilizing a population of children in the United States to test the hypothesis that the critical time periods during tooth formation when excessive fluoride intake may result in dental fluorosis can he identified. The specific aims will be to: 1, identify and recrnit approximately 300 children (7-12 years-of-age) who are lifetime residents of a community whose communal water supply has undergone an alteration in fluoride content which should result in a definable variation in the degree of dental fluorosis on the labial surfaces of the permanent teeth of these children; 2, examine, in the Year 2000, the labial surfaces of the available permanent dentition of these children using established dental fluorosis indices to identify the periods of susceptibility for the development of dental fluorosis and to also determine the prevalence of dental fluorosis; 3, gather retrospective data by means of a questionnaire to determine sources of fluoride ingestion during infancy and early childhood; and, 4, develop a data analysis plan to identify the time periods associated with the development of dental fluorosis in the permanent dentition and determine the prevalence of dental fluorosis in these children for comparison to data previously collected in the community by the investigators. These children will be essentially lifetime residents of Lowell, Indiana and will have used the communal water supply as their primary source of drinking water. They will be examined using the Tooth Surface Index of Fluorosis and the Chronological Fluorosis Assessment. Data will also be collected to determine each panelist's level of fluoride ingestion during early childhood. Analyses of the data will allow the investigators to confirm the critical time periods for the development for the remaining dentition. This investigation will be the first in a series of studies relating to this topic to take advantage of this timely opportunity and this unique population.